1. Field of the Invention
The present invention relates to electronic circuits based on molecular transistors, generally used in place of semiconductors. More particularly, the invention relates to a unique method of wiring of a three-terminal molecule (or an aggregate thereof) to serve as an electronic transistor, containing a gate electrode, a source electrode, and a drain electrode. The source electrode and drain electrode are fabricated from one metal and the gate electrode is fabricated from another metal. The usage of molecular properties in this context provides significant advantages over the fabrication methods of the prior art.
2. Description of the Prior Art
Numerous innovations for electronic circuits have been provided in the prior art that are described as follows. Although these innovations may be suitable for the specific individual purposes to which they address, they differ from the present invention as hereinafter contrasted. The following is a summary of those prior art patents most relevant to the invention at hand, as well a description outlining the differences between the features of the present invention and those of the prior art.
1. U.S. Pat. No. 6,339,227, Invented by Ellenbogen, Entitled “Monomolecular Electronic Device”
In the patent to Ellenbogen, a monomolecular electronic device is provided which includes a molecular diode having at least one barrier insulating group chemically bonded between a pair of molecular ring structures to form a pair of diode sections, at least one dopant group chemically bonded to one of the pair of diode sections, and a molecular gate structure chemically bonded to the one diode section for influencing an intrinsic bias formed by the at least one dopant group. The device thus produced operates as a molecular electronic transistor, exhibiting both switching and power gain. By adding yet another insulating group to the other of the diode sections, an electrical resistance is formed to define an output which represents an inverter or NOT gate function. The NOT gate can be chemically bonded to molecular diode-diode logic structures to form a single molecule that exhibits complex Boolean functions and power gain.
2. U.S. Pat. No. 4,912,531, Invented by Reed et al., Entitled “Three-Terminal Quantum Device”
The patent to Reed et al. descries a three-terminal quantum well device, which functions somewhat analogously to an MOS transistor. That is, the three terminals of the device can generally be considered as source, gate, and drain. An output contact is connected by tunneling to a number of parallel chains of quantum wells, each well being small enough that the energy levels in the well are quantized discretely. In each of these chains of wells, the second well is coupled to a common second conductor, and the first well is electronically coupled to a common first conductor.
3. U.S. Pat. No. 6,259,277, Invented by Tour, et al., Entitled “Use Of Molecular Electrostatic Potential To Process Electronic Signals”
The Tour et al. invention is a design paradigm for molecular scale electronic systems wherein electronic information is transmitted and processed, and electronic logic is obtained by changing the electrostatic potential of a molecule. The signal may be restored using an external potential through the underlying substrate. Several convergent synthetic routes are shown to conjugated molecules with various potential electronic device applications including a two-terminal molecular wire with a transport barrier, a molecular wire with two transport barriers, three-terminal junctions, three-terminal structures with switch-like possibilities, and four-terminal systems that could serve as logical gates without the use of multiple transistors. Ab initio computational methods are used to show that molecules can be considered active electronic devices able to transfer the information from one molecule to another, the electrostatic potential can also be used as a tool to perform logical operations, and that the molecules synthesized here could perform the functions for which they were designed.
4. U.S. Pat. No. 5,879,973, Invented by Yanai et al., Entitled “Method For Fabricating Thin-Film Transistor”
To form a contact layer on source and drain electrodes of a stagger-type TFT, a conductive material is selectively sticked to the surface of the source and drain electrodes and a contact layer is selectively deposited by using the conductive material as growth species to form an active semiconductor layer on the contact layer. For an inverted-stagger-type TFT, a conductive material is selectively deposited on the surface of a contact layer to use the selectively deposited conductive material as source and drain electrodes so that patterning is unnecessary. To selectively deposit a contact layer of a TFT by alternately repeating etching and deposition, the temperature for the etching is set to 200.degree. C. or lower. A contaminated layer on the surface of a semiconductor film serving as an active semiconductor layer and contact layer of a TFT is removed by plasma at the temperature of 200.degree. C. or lower. For a stagger-type thin-film transistor, the hydrogen or halogen content of an insulating film serving as the substrate of source and drain electrodes is increased. For an inverted-stagger thin-film transistor, the hydrogen or halogen content of an insulating film serving as a channel protective film is increased. Thus, the etching rate of the surfaces of these insulating films by plasma increases.
5. U.S. Pat. No. 6,320,200, Invented by Reed et al., Entitled “Sub-Nanoscale Electronic Devices And Processes”
The patent to Reed et al. describes an integrated circuit structure including a plurality of transistors; a plurality of thin-film conductor interconnects, interconnected to form electronic circuits in a predetermined electrical configuration; and a plurality of pairs of contact pads, connected to the thin-film conductor interconnects, each adjacent pair of contact pads including a first pad of a first conductive material and a second pad of a second conductive material, and being electrically connected only by a conductive oligomer of a precisely determined number of units.
6. U.S. Pat. No. 6,091,267, Invented by Palm et al., Entitled “Logic Circuits”
The patent to Palm et al. describes a logic circuit having at least a first input terminal and at least a first output terminal, comprises at least a first and a second electron-wave Y-branch switch, each having a source, a first drain, a second drain, and at least a first gate for switching a source current between the first and the second drain. The sources of said first and second Y-branch switches are adapted to be connected to a high voltage supply and a low voltage supply, respectively. The first gates of said first and second Y-branch switches are interconnected, and the interconnection point between said first gates constitutes said first input terminal. The first drain of the first Y-branch switch is connected to the second drain of the second Y-branch switch, and the second drain of the first Y-branch switch is connected to the first drain of the second Y-branch switch. The interconnection point between said second drain of the first Y-branch switch and said first drain of the second Y-branch switch constitutes said first output terminal.
7. U.S. Pat. No. 6,430,511, Invented by Tour et al., Entitled “Molecular Computer”
In the patent to Tour et al., a molecular computer is formed by establishing arrays of spaced-apart input and output pins on opposing sides of a containment, injecting moleware in solution into the containment and then allowing the moleware to bridge the input and output pins. Moleware includes molecular alligator clip-bearing 2-, 3-, and molecular 4-, or multi-terminal wires, carbon nanotube wires, molecular resonant tunneling diodes, molecular switches, molecular controllers that can be modulated via external electrical or magnetic fields, massive interconnect stations based on single nanometer-sized particles, and dynamic and static random access memory (DRAM and SRAM) components composed of molecular controller/nanoparticle or fullerene hybrids. The current-voltage characteristics that result from the bridging between input and output arrays can be ascertained using another computer to identify the bundles of inputs and corresponding outputs that provide a truth table for the specific functions of the computer.
8. U.S. Pat. No. 6,518,168, Invented by Clem et al., Entitled “Self-Assembled Monolayer Directed Patterning Of Surfaces”
The patent to Clem et al. describes a technique for creating patterns of material deposited on a surface involves forming a self-assembled monolayer in a pattern on the surface and depositing, via chemical vapor deposition or via sol-gel processing, a material on the surface in a pattern complementary to the self-assembled monolayer pattern. The material can be a metal, metal oxide, or the like. The surface can be contoured, including trenches or holes, the trenches or holes remaining free of self-assembled monolayer while the remainder of the surface is coated. When exposed to deposition conditions, metal or metal oxide is deposited in the trenches or holes, and remaining portions of the article surface remain free of deposition. The technique finds particular use in creation of conductive metal pathways selectively within holes passing from one side of a substrate to another.
9. U.S. Pat. No. 5,487,792, Invented by King et al., Entitled “Molecular Assemblies As Protective Barriers And Adhesion Promotion Interlayer”
In the patent to King et al., a protective diffusion barrier having adhesive qualifies for metalized surfaces is provided by a passivating agent having the formula HS—(CH.sub.2).sub.11—COOH Which forms a very dense, transparent organized molecular assembly or layer that is impervious to water, alkali, and other impurities and corrosive substances that typically attack metal surfaces.
10. U.S. Pat. No. 4,690,715, Invented by Allara et al., Entitled “Modification Of the Properties Of Metals”
The use of modifiers such as disulfides and phosphines is particularly effective in modifying the properties of metals such as noble metals and silver. For example, disulfides are useful for modifying the properties of gold and silver while phosphines are useful for metals such as platinum and palladium. Through treatment with a suitable modifier it is possible to change properties such as the wetting and adhesion properties of the treated metal. Additionally, the use of modifiers to treat a desired substrate enhances formation of continuous metal films on this substrate.
11. U.S. Pat. No. 5,034,192, Invented by Wrighton et al., Entitled “Molecule-Based Microelectronic Devices”
In the patent to Wrighton et al., several types of new microelectronic devices including diodes, transistors, sensors, surface energy storage elements, and light-emitting devices are disclosed. The properties of these devices can be controlled by molecular-level changes in electroactive polymer components. These polymer components are formed from electrochemically polymerizable material whose physical properties change in response to chemical changes, and can be used to bring about an electrical connection between two or more closely spaced microelectrodes. Examples of such materials include polypyrrole, polyaniline, and polythiophene, which respond to changes in redox potential. Each electrode can be individually addressed and characterized electrochemically by controlling the amount and chemical composition of the functionalizing polymer. Sensitivity of the devices may be increased by decreasing separations between electrodes as well as altering the chemical environment of the electrode-confined polymer. These very small, specific, sensitive devices provide means for interfacing electrical and chemical systems while consuming very little power.
12. U.S. Pat. No. 5,017,975, Invented by Ogawa, Entitled “Organic Electronic Device With A Monomolecular Layer Or Multi-Monomolecular Layer Having Electroconductive Conjugated Bonds”
The Ogawa invention provides an organic electronic device characterized by comprising a monomolecular or built-up multi-monomolecular layer having an insulating layer and an electroconductive conjugated bonds disposed between a first electrode and both a second and a third electrodes formed on a substrate, said device being operated by applying an voltage between said first electrode and said second electrode or said third electrode as well as between said second electrode and said third electrode, varying the voltage between said first electrode and said second electrode or said third electrode to control the electroconductivity of said electroconductive conjugated bonds via said insulating layer, whereby an electric current flowing across said electroconductive conjugated bonds between said second electrode and said third electrode is controlled, where said monomolecular layer is produced by utilizing the LB method or a chemical adsorption technique.
13. U.S. Pat. No. 6,482,639, Invented by Snow et al., Entitled “Microelectronic Device And Method For Label-Free Detection And Quantification Of Biological And Chemical Molecules”
The patent to Snow et al. describes a molecular recognition-based electronic sensor, which is a gateless, depletion mode field effect transistor consisting of source and drain diffusions, a depletion-mode implant, and insulating layer chemically modified by immobilized molecular receptors that enables miniaturized label-free molecular detection amenable to high-density array formats. The conductivity of the active channel modulates current flow through the active channel when a voltage is applied between the source and drain diffusions. The conductivity of the active channel is determined by the potential of the sample solution in which the device is immersed and the device-solution interfacial capacitance. The conductivity of the active channel modulates current flow through the active channel when a voltage is applied between the source and drain diffusions. The interfacial capacitance is determined by the extent of occupancy of the immobilized receptor molecules by target molecules. Target molecules can be either charged or uncharged. Change in interfacial capacitance upon target molecule binding results in modulation of an externally supplied current through the channel.
14. U.S. Pat. No. 5,536,573, Invented by Rubner et al., Entitled “Molecular Self-Assembly Of Electrically Conductive Polymers”
In the patent to Rubner et al., a thin-film heterostructure bilayer is formed on a substrate by a molecular self-assembly process based on the alternating deposition of a p-type doped electrically conductive polycationic polymer and a conjugated or nonconjugated polyanion or water soluble, non-ionic polymer has been developed. In this process, monolayers of electrically conductive polymers are spontaneously adsorbed onto a substrate from dilute solutions and subsequently built-up into multilayer thin films by alternating deposition with a soluble polyanion or water soluble, non-ionic polymer. In contrast to a deposition process involving the alternate self-assembly of polycations and polyanions, this process is driven by non-covalent bonded attractions (for example, ionic and hydrogen bonds) developed between a p-type doped conducting polymer and a polymer capable of forming strong secondary bonds. The net positive charge of the conducting polymer can be systematically adjusted by simply varying its doping level. Thus, with suitable choice of doping agent, doping level and solvent, it is possible to manipulate a wide variety of conducting polymers into uniform multilayer thin films with layer thicknesses ranging from a single monolayer to multiple layers.
15. U.S. Pat. No. 6,492,096, Invented by Liu et al., Entitled “Patterned Molecular Self Assembly”
In the patent to Liu et al., a patterned molecular self-assembly is provided. The patterned molecular self-assembly comprises a support having an exposed patterned surface and a non-patterned surface. A compound is selectively adsorbed on the exposed patterned surface. The compound may comprise a first compound selectively adsorbed on the exposed patterned surface and a second compound selectively adsorbed on the first compound to form at least one bilayer. The patterned molecular self-assembly may further comprise a first set of bilayers and a second set of bilayers wherein the first set of bilayers has a different composition than the second set of bilayers.
Generally, with regard to all prior art, the act of further miniaturizing devices via conventional semiconductor fabrication has become increasingly difficult, with associated rising costs therewith. Thus, two types of molecular transistors have been described in the prior art as alternatives to semiconductor fabrication.
The first type of molecular transistor is based on a double-well potential molecule, which contains two elongated chains placed next to one another perpendicularly. Such is illustrated in FIG. 1, which shows the molecule without the connecting electrodes.
In this instance of FIG. 1, one of the chains lacks an electron and is conductive, while the other chain is insulating. By application of a perpendicular electric field, it is then possible to switch the position of the electron hole to the insulating chain, thus rendering it conductive. [See A. Aviram, Journal of the American Chemical Society, 1998, 110, 5687.] This process is equivalent to switching the conductivity of a field-effect transistor. A planar configuration for this device is shown in FIG. 2, which again shows the molecule without the connecting electrodes. [See A. Aviram, Molecular Crystals and Liquid Crystals, 1993, 234, 13.]
The second type of molecular transistor of the prior art is categorized as one elongated molecule placed between a total of four electrodes, as shown in FIG. 3. [See M. Di Ventra, S. T. Pentelides, and N. Lang, Applied Physics Letters, 2000, 7, 3448.]
In general, the desired migration from semiconductor devices to molecular devices requires the adoption of new techniques and methods from building the molecular-integrated circuits. It is widely accepted that the changeover will utilize the unique technique of self-assembly. [See R. G. Nuzzo and D. L. Allara, Journal Of The American Chemical Society, 1983, 105, 4481; D. L. Allara et al., Annals of the New York Academy of Sciences, A. Aviram and M. A. Ratner, Editors, 1998, 852, 349.] Importantly, this technique is based on the fact that certain chemical groups have a strong affinity for specific metal surfaces, and will therefore form strong chemical bonds therewith.
To provide an example of the above, the sulfur group (—SH) generally binds spontaneously to gold, platinum, silver, and copper. This allows same to form single monolayers of the organic or organometallic compound on the metal surface. Such method has been successfully used to place molecules between adjacent electrodes and to make electrical contacts to them. [See M. A. Reed, C. Zhou, C. J. Muller, T. P. Burginn and J. M. Tour, Science, 1997, 278, 252.]
The binding groups referred to above are called “alligator clips.” The first publication proposing the use of self-assembly for molecular-electronic circuits appeared in 1991. [See A. Aviram, International Journal of Quantum Chemistry, 1992, 5, 1615.]
The method has since been accepted as the only practical method for making “ohmic” contacts to the molecules. According to this concept, the formation of molecular-electronic circuits is based on the following steps:                Step 1: The molecules are synthesized and provided with alligator clips in the positions where the molecule is intended to be connected to the circuit electrodes;        Step 2: A network of metallic electrodes is prepared on an insulating surface according to the circuit specifications. The network contains gaps in all locations where the molecules will be inserted. The size of the gaps must be a n effective match to the size of the molecules which must be contained in the gap; the metal composition is intended to have an affinity to the alligator-clips on the molecules; and        Step 3: The metal network is brought into contact with a solution of the molecules, and self-assembly occurs spontaneously. More particularly, the molecules insert themselves in the appropriate gaps. After such attachment occurs, the unbound molecules are rinsed off. This step effectively completes the circuit formation.        
In this context it must be understood that the transistor is the device that made possible the electronic revolution that is in progress today. If molecular electronics is to supplement or exceed the capabilities of the semiconductor industry, there must be a cost-effective and reliable way to wire three-terminal molecular transistors into integrated circuits. The present invention teaches how to achieve this important goal.
As outlined above, the self-assembly technique is employed to direct the molecules to the respective locations in the circuit and to attach them to the electrodes. However, the examples found in the current literature show how to attach molecules to only one or two terminals. Specific examples for simultaneous attachment of molecules to three electrodes do not exist in the prior art.
Because the transistor molecule contains three terminals, there is a significant need for a method to attach all three terminals in the proper order. Specifically, because of the C2v symmetry of the molecules, the source and drain terminals on the molecule are symmetric and interchangeable, while the gate terminal must be connected to a specified gate electrode.